The present invention relates to vacuum cleaner bags, particularly vacuum cleaner bags having filtration layers.
Traditionally, vacuum cleaner bags were constructed with cellulosic paper, generally relatively high basis weight paper. These paper bags are advantageous in terms of their cost. However, relatively recently it has become clear that these bags discharge a significant amount of respirable particulate materials, specifically particles having a diameter of less than 10 microns. These size particles remain airborne for long periods of time and contain many allergens. As such these fine respirable particles are placed into the indoor atmosphere by the vacuum cleaner causing significant health concerns for people with allergies and the like. To address these concerns a number of patents suggest laminating cellulosic bags with inner filtration layers, specifically fine particle synthetic fiber filter material layers, such as meltblown nonwovens, spunbond webs or combinations thereof For example, U.S. Pat. No. 3,498,031 proposes adding a small felt-like layer onto an inner surface of a paper bag, allegedly this felt-like material intercepts dust circulating within the bag. In order to avoid undue increases in pressure drop, the filter material is only placed at specific locations and certain other areas of the bag are not provided with a filter material. This construction would allow significant amounts of particles to still bypass the filter felt. It also has been proposed to modify traditional paper vacuum cleaner bags by providing a continuous inner liner of a synthetic fibrous filter medium. For example, U.S. Pat. No. 5,080,702 proposes lining a paper bag with a synthetic fibrous filter medium such as a meltblown web and in U.S. Pat. No. 5,306,534 it is suggested that this type of synthetic filter medium bag liner can be electret charged. A similar filter lined paper bag structure is also proposed in European Pat. No. 338479 which describes a filter layer formed of a meltblown nonwoven material or microglass fiber material, which filter material may contain an electret charge. A method for making a filter lined paper bag of the above type is disclosed in U.S. Pat. No. 5,437,910. This patent states that it is important to have paper layer to paper layer overlap at the seams to ensure a sufficiently strong seam. This is accomplished by offsetting the filter liner at one edge of the paper outer layer.
In an attempt to move away from paper altogether, some patents have proposed vacuum cleaner bags formed exclusively of synthetic materials. However, generally the seams for these bags are still described as made by sewing or adhesive bonding as are conventional paper bags. U.S. Pat. No. 4,589,894 proposes a filter layer that comprises a web of random synthetic polymeric microfibers, less than 10 microns in diameter on average. This filter layer web has a specific range of basis weights and air permeability. Further, in order to protect this relatively fragile filter layer, the filter layer is sandwiched between two more resilient outer nonwoven layers, for example, spun bond nonwoven webs. U.S. Pat. No. 4,917,942 also suggests forming a vacuum cleaner bag with synthetic materials. The vacuum cleaner bags produced from this media are allegedly producable on conventional paper bag converting equipment. The filter material laminate comprises a microfiber web of synthetic polymers which web has been directly adhered to a support web. The microfiber web is charged to induce electrets, which provides a filter media having high capture efficiency for fine submicron particles with a relatively low pressure drop.
U.S. Pat. Nos. 5,306,534 and 5,244,703 (Bosses) describes a charged synthetic fiber filter web which is attached permanently by adhesives to a textile fabric to form a reusable vacuum cleaner bag allegedly with high filter efficiency. The electret charged filter web material is a charged melt blown microfiber web (like the '942 patent) placed between two outer support layers (like the '894 patent), specifically described as spunbond materials. The charged meltblown microfiber filter web layer(s) and spunbond layer(s) are described as pattern bonded together.
PCT Publication WO 93/21812 (Van Rossen) describes a vacuum cleaner bag produced with materials such as described in U.S. Pat. No. 4,917,942, which is provided with a scrim layer on the face opposite the vacuum cleaner hose inlet to provide specific abrasion resistance against large sand particles and the like. The scrim layer is bonded to the filter layer only at the vacuum cleaner bag end seams simplifying manufacturing. The seams are stated as formed by welding.
U.S. Pat. No. 5,647,881 proposes a high efficiency vacuum cleaner bag comprising an inner diffusion layer which overlays a synthetic fiber filtration layer and an underlying nonwoven support layer. The inner diffusion layer is purposely not bonded to the underlying filter layer and supporting layer. The resulting bag provides both high efficiency and reduction in particle emissions under shock loading conditions. The seams of the bag can be formed by heat, ultrasonics or adhesives.
Although the above all synthetic material filter bag type constructions provide significant increases in efficiency over traditional paper bags, or even filter layer lined paper bags, there is still a desire for high levels of filtration performance coupled with good mechanical performance at lower costs.